1. Field of the Invention
The present invention relates to a die bonding sheet sticking apparatus and relates to a method of sticking a die bonding sheet. In these die bonding sheet sticking apparatus and method of sticking a die bonding sheet, in the process for producing small electronic components, for example, semiconductor chips, a die bonding sheet capable of functioning as an adhesive material for die bonding is stuck to a back surface of wafer at the time of die bonding of semiconductor chips after dicing onto a lead frame.
2. Description of the Prior Art
In the conventional production of a wafer of semiconductor such as silicon (hereinafter simply referred to as xe2x80x9cwaferxe2x80x9d), the wafer is first produced in the form of a disk having a large diameter. A circuit pattern is formed on a surface of the wafer, and the surface of the circuit pattern is protected by a protective tape. The back side of the wafer is ground, and stuck onto a ring frame with a pressure sensitive adhesive sheet interposed therebetween. The protective tape is detached from the surface of the circuit pattern, and the wafer is cut apart into a multiplicity of dice formed chips by the use of a dicing cutter (dicing). In this state, the wafer chips are transferred to the subsequent steps such as cleaning, drying and die bonding steps.
In the conventional method of sticking a pressure sensitive adhesive sheet to a back surface of wafer, as shown in FIG. 14, wafer W is disposed on retention table 200. Pressure sensitive adhesive sheet 202 consisting of base sheet 204 and pressure sensitive adhesive layer 206 is stuck to back surface W3 of the wafer W. The pressure sensitive adhesive sheet 202 is cut by rotating upward arranged cutter 210 along the outline (circumference) W4 of the wafer W.
However, recently, the reduction of the thickness of semiconductor chips such as IC cards is increasingly demanded. The demand for semiconductor chips whose thickness has been reduced to about 100-50 xcexcm from the conventional about 300 xcexcm is increasing in recent years. For obtaining such semiconductor chips, it is needed to produce extremely thin wafers having the above reduced thickness.
In the use of such extremely thin wafers, there is the danger of flawing of circumferential portion W4 of the wafer W or cracking of the wafer W at the cutting of the pressure sensitive adhesive sheet 202 with the use of the cutter 210. Moreover, there is the sheet stuck at V notch portion provided on the wafer, so that there would occur failure in the recognition of wafer alignment effected in a later step.
For the purpose of avoiding such wafer flawing or wafer cracking, it is also practiced in the prior art to cut a pressure sensitive adhesive sheet along the outline of wafer in a separate step in advance and stick the cut pressure sensitive adhesive sheet to a back surface of the wafer.
Further, in the prior art, die bonding is carried out by using an ultraviolet curable pressure sensitive adhesive sheet as the pressure sensitive adhesive sheet. In this die bonding, where semiconductor chips cut apart into a multiplicity of chips are die bonded (transfer mounted) to a lead frame, ultraviolet is applied to the ultraviolet curable pressure sensitive adhesive sheet. As a result, the adhesive strength of the ultraviolet curable pressure sensitive adhesive sheet is lowered so that die bonding is practiced by using suction collets.
Still further, at the time of die bonding, it is known to separately coat a lead frame with an adhesive and effect die bonding of semiconductor chips onto the coated lead frame.
However, the current situation is that, in any case, another step is needed to thereby cause the process to be complex, bringing about a cost increase.
The present invention provides a die bonding sheet sticking apparatus for wafer which, at the time of die bonding of semiconductor chips onto a lead frame, after dicing, a sequence of steps for sticking a die bonding sheet capable of functioning as an adhesive for die bonding to a back surface of wafer can be performed in a continuous and automatic manner without wafer damaging or cracking. The present invention also provides a method of sticking a die bonding sheet with the use of the die bonding sheet sticking apparatus.
The present invention has been made with a view toward solving the above problems of the prior art and attaining the above object. The die bonding sheet sticking apparatus of the present invention includes:
a wafer supply section for accommodating a plurality of wafers therein,
a wafer conveyance section including conveyance means for taking out a wafer from the wafer supply section and conveying the wafer,
an alignment section for positioning the wafer taken out from the wafer supply section via the wafer conveyance means of the wafer conveyance section,
a sheet sticking section for conveying the wafer arranged for given reference position at the alignment section via conveying means and for sticking a die bonding sheet to a back surface of the wafer by heating, said die bonding sheet comprising a release sheet and a base provided with heat-sensitive adhesive layer, and
a sheet peeling section including sheet peeling means for peeling the release sheet of the die bonding sheet from the wafer having the die bonding sheet stuck thereto at the sheet sticking section,
wherein the sheet sticking section comprises:
cutting means capable of, prior to the sticking of the die bonding sheet to the back surface of the wafer, cutting the base provided with heat-sensitive adhesive layer of the die bonding sheet in conformity with an outline of the wafer,
said cutting means capable of cutting the base provided with heat-sensitive adhesive layer in the direction of a width of the die bonding sheet with a spacing of given distance from a rear end portion of the wafer in the direction of conveyance of the wafer so as to form a leaf portion; and
leaf detaching means capable of, prior to the sticking of the die bonding sheet to the back surface of the wafer, detaching only the leaf portion, corresponding to portion outside the outline of the wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet after the cutting by said cutting means.
The above structuring of the apparatus enables continuously and automatically carrying out a series of operations including taking out a wafer from a wafer cassette wherein a plurality of wafers are accommodated, alignment for positioning the wafer, sticking a die bonding sheet comprising a release sheet and a base provided with heat-sensitive adhesive layer to the back of the wafer, detaching the release sheet of the die bonding sheet, and accommodating the wafer in a wafer cassette.
The die bonding sheet also functions not only as a protective tape at the time of dicing but also as an adhesive for die bonding at the time of die bonding of semiconductor chips to a lead frame after dicing, because the die bonding sheet comprises a release sheet and a base provided with heat-sensitive adhesive layer.
Therefore, as different from the prior art, it is not needed to apply an adhesive to a lead frame at the time of die bonding. In the present invention, only heating the die bonding sheet enables not only picking up, by suction, semiconductor chips with the use of suction collets but also direct thermocompression bonding because the heat-sensitive adhesive layer of the die bonding sheet also functions as an adhesive for a lead frame.
Also, the base provided with heat-sensitive adhesive layer of the die bonding sheet is cut in conformity with the outline of wafer before the sticking of the die bonding sheet to the back surface of the wafer. Therefore, there is no danger of flawing of a peripheral portion of wafer or wafer cracking as experienced at the cutting of die bonding sheet with a cutter in the prior art. Moreover, as different from the prior art, it is not needed to cut the die bonding sheet by a separate operation in advance.
Further, prior to the sticking of the die bonding sheet to the back surface of the wafer, only the leaf portion, corresponding to portion outside the outline of wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet after the cutting with the cutting means is detached by the use of leaf detaching means. Therefore, at the sticking of heated wafer back surface to the die bonding sheet, any fusion bonding between an outline portion of the wafer and the leaf portion corresponding to portion outside the outline of wafer can be avoided. Consequently, the release sheet of the die bonding sheet can be easily detached, without any hindrance, from the wafer.
In the die bonding sheet sticking apparatus according to the present invention, the cutting means may comprise:
a cutting blade unit including a cutting blade shaped in conformity with the outline of the wafer and a cutting blade provided in the direction of a width of the die bonding sheet with a spacing of given distance from a rear end portion of the wafer in the direction of conveyance of the wafer, the cutting blade unit being vertically movable and lifted upward from under the die bonding sheet so that the cutting blade is brought into contact with the base provided with heat-sensitive adhesive layer of the die bonding sheet, and
a cutting press unit adapted to, upon lifting of the cutting blade unit upward, press the die bonding sheet downward from above the die bonding sheet to thereby effect cutting of only the base provided with heat-sensitive adhesive layer of the die bonding sheet.
This structuring enables easily and accurately cutting of the base provided with heat-sensitive adhesive layer of the die bonding sheet into portion with an outline identical with that of the wafer and the leaf portion corresponding to portion outside the outline of wafer.
Further, in the die bonding sheet sticking apparatus according to the present invention, the leaf detaching means may include a temperature regulating unit capable of cooling or heating the die bonding sheet from its release sheet side at the time of detaching only the leaf portion, corresponding to portion outside the outline of wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet.
For example, there can be mentioned the case wherein the heat-sensitive adhesive layer of the die bonding sheet is constituted of an epoxy resin while the release sheet of the die bonding sheet is constituted of polyethylene terephthalate (PET). If the heat sensitive adhesive layer is constituted of an epoxy resin, the adherence between the base provided with heat-sensitive adhesive layer and the release sheet may be increased depending on the change of ambient temperature to thereby cause it difficult to peel the base provided with heat-sensitive adhesive layer.
However, the regulating of the temperature of die bonding sheet by cooling or heating in conformity with the condition of the die bonding sheet according to the present invention enables stabilizing the adherence between the release sheet and the heat-sensitive adhesive layer. As a result, the peeling of the release sheet can be stably effected at the time of peeling. That is, the adherence between the base provided with heat-sensitive adhesive layer and the release sheet can be stabilized without any change thereof, so that only the leaf portion, corresponding to portion outside the outline of wafer, of the base provided with heat-sensitive adhesive layer can be easily peeled.
Still further, in the bonding sheet sticking apparatus of the present invention, the leaf detaching means may include a suction detaching unit adapted to, after the cutting by the cutting means, detach only the leaf portion, corresponding to portion outside the outline of wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet by suction from thereunder.
This structuring enables easily detaching only the leaf portion, corresponding to portion outside the outline of wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet.
Still further, in the die bonding sheet sticking apparatus of the present invention, the leaf detaching means may include a removing unit capable of removing the leaf portion, corresponding to portion outside the outline of wafer, having been detached by the suction detaching unit, from the suction detaching unit.
This structuring enables easily removing the leaf portion, corresponding to portion outside the outline of wafer, having been detached by the suction detaching unit, from the suction detaching unit.
Furthermore, in the die bonding sheet sticking apparatus of the present invention,
the suction detaching unit may include suction members shaped like a comb, and
the removing unit may include shake down members shaped like a comb which can be inserted in interstices of the comblike suction members of the suction detaching unit,
so that the leaf portion corresponding to portion outside the outline of wafer, having been detached by suction by the comblike suction members of the suction detaching unit, is removed from the suction detaching unit by inserting the comblike shake down members of the removing unit in the interstices of the comblike suction members of the suction detaching unit from thereunder.
This structuring enables easily and securely removing the leaf portion corresponding to portion outside the outline of wafer, having been detached by suction by the comblike suction members of the suction detaching unit, from the suction detaching unit only by inserting the comblike shake down members of the removing unit in the interstices of the comblike suction members of the suction detaching unit from thereunder.
Therefore, failure to remove the leaf portion from the suction detaching unit can be avoided with the result that continuous operation of the die bonding sheet sticking apparatus of the present invention would not be hindered to thereby attain an enhancement of production efficiency.
Still further, in the die bonding sheet sticking apparatus of the present invention, the sheet sticking section may include:
a mount table adapted to mount the wafer thereon and including a heater capable of heating the wafer, and
a sticking press unit capable of pressing the die bonding sheet having been heated by the mount table downward from above the die bonding sheet so as to stick the base provided with heat-sensitive adhesive layer of the die bonding sheet to the back surface of the wafer disposed on the mount table.
This structuring enables heating the die bonding sheet and enables easily and securely sticking the base provided with heat-sensitive adhesive layer to the back surface of the wafer.
Moreover, in the die bonding sheet sticking apparatus of the present invention, the mount table may protrude upward at a peripheral portion thereof to thereby provide a suction part adapted to fix a peripheral portion of the surface of wafer by suction,
the mount table further including an air blow space part surrounded by the suction part and adapted to support the surface of wafer upward from thereunder by compressed air.
This structuring enables avoiding contact of the mount table with the circuit pattern lying on the surface of the wafer, so that damaging of the circuit pattern can be prevented. Further, the entirety of the wafer is supported upward by compressed air, so that the pressing downward by means of the sticking press unit at the time of sticking the die bonding sheet would not bring about bubbling between the die bonding sheet and the back surface of the wafer and would not cause wafer cracking, breakage or damaging.
Moreover, in the die bonding sheet sticking apparatus of the present invention, the sticking press unit may include a fixed roller and a press moving roller,
the fixed roller capable of retaining the die bonding sheet at a position upstream of the wafer,
the press moving roller adapted to be moved downstream to thereby effect sticking of the die bonding sheet to the back surface of the wafer.
By virtue of this structuring, the fixed roller retains the die bonding sheet at a position upstream of the wafer while the press moving roller is moved downstream, so that any air between the back surface of the wafer and the die bonding sheet is expelled from the downstream side. Consequently, trapping of air between the back surface of the wafer and the die bonding sheet can be avoided. Further, by inclining the die bonding sheet, sticking with a given tension can be effected without any wrinkling. Therefore, the die bonding sheet can be securely stuck to the back surface of the wafer.
In the die bonding sheet sticking apparatus of the present invention, the press moving roller may be provided with a heating unit.
This structuring enables further heating the die bonding sheet by means of the heating unit of the press moving roller, so that the base provided with heat-sensitive adhesive layer can be stuck to the back surface of the wafer more easily and more securely.
Still further, in the die bonding sheet sticking apparatus of the present invention, the sheet peeling section may include a mount table adapted to mount the wafer thereon,
the mount table protruding upward at a peripheral portion thereof to thereby provide a suction part adapted to fix a peripheral portion of the surface of wafer by suction,
the mount table further including an air blow space part surrounded by the suction part and adapted to support the surface of wafer upward from thereunder by compressed air.
This structuring enables avoiding contact of the mount table with the circuit pattern lying on the surface of the wafer, so that damaging of the circuit pattern can be prevented. Further, the entirety of the surface of wafer is supported upward by compressed air, so that, at the time of peeling the release sheet of the die bonding sheet, there would not occur wafer cracking, breakage or damaging.
In the die bonding sheet sticking apparatus of the present invention, still further, the sheet peeling means may include a fixed roller and a pair of detaching moving rollers,
the fixed roller capable of retaining the die bonding sheet at its downstream side,
the pair of peeling moving rollers adapted to have the die bonding sheet wound round and sandwiched between them and to move upstream of the die bonding sheet so that the release sheet of the die bonding sheet is peeled from the wafer.
This structuring enables peeling the release sheet of the die bonding sheet from the wafer securely and easily.
In another aspect of the present invention, there is provided a method of sticking a die bonding sheet, comprising:
a die bonding sheet cutting step comprising, prior to sticking of a die bonding sheet comprising a release sheet and a base provided with heat-sensitive adhesive layer to a back surface of wafer, cutting only the base provided with heat-sensitive adhesive layer of the die bonding sheet in conformity with an outline of the wafer,
said die bonding sheet cutting step being cutting the base provided with heat-sensitive adhesive layer in the direction of a width of the die bonding sheet with a spacing of given distance from a rear end portion of the wafer in the direction of carry of the wafer so as to form a leaf portion; and
a leaf detaching step comprising detaching only the leaf portion, corresponding to portion outside the outline of the wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet after the cutting in the die bonding sheet cutting step,
a die bonding sheet sticking step comprising, after the cutting in conformity with the outline of the wafer in the die bonding sheet cutting step and further after the detaching of only the leaf portion, corresponding to portion outside the outline of the wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet, sticking the base provided with heat-sensitive adhesive layer of die bonding sheet which has an outline conforming to that of the wafer, while heating, to the back surface of the wafer, and
a sheet peeling step comprising peeling the release sheet of the die bonding sheet from the wafer having the die bonding sheet stuck thereto in the die bonding sheet sticking step.
In this method, the die bonding sheet functions not only as a protective tape at the time of dicing but also as a pressure sensitive adhesive for die bonding at the time of die bonding of semiconductor chips to a lead frame after dicing, because the die bonding sheet comprises a release sheet and a base provided with heat-sensitive adhesive layer.
Therefore, as different from the prior art, it is not needed to paste an adhesive to a lead frame at the time of die bonding. In the present invention, only heating the die bonding sheet enables not only picking up, by suction, semiconductor chips with the use of suction collets but also direct thermocompression bonding because the base provided with heat-sensitive adhesive layer of the die bonding sheet functions as an adhesive for a lead frame.
Also, the base provided with heat-sensitive adhesive layer of the die bonding sheet is cut in conformity with the outline of wafer before the sticking of the die bonding sheet to the back surface of the wafer. Therefore, there is no danger of flawing of a peripheral portion of wafer or wafer cracking as experienced at the cutting of die bonding sheet with a cutter in the prior art. Moreover, as different from the prior art, it is not needed to cut the die bonding sheet by another operation in advance.
Further, prior to the sticking of the die bonding sheet to the back surface of the wafer, only the leaf portion, corresponding to portion outside the outline of wafer, of the base provided with heat-sensitive adhesive layer of the die bonding sheet after the cutting in the cutting step is detached in the leaf detaching step. Therefore, at the sticking of heated wafer back surface to the die bonding sheet, any fusion bonding between an outline portion of the wafer and the leaf portion corresponding to portion outside the outline of wafer can be avoided. Consequently, the release sheet of the die bonding sheet can be easily detached, without any hindrance, from the wafer.